Bioaccumulation of Potential Harmful Elements in Fossorial Water Voles Inhabiting Non-Polluted Crops

Although the health risks associated with exposure to potentially harmful elements (PHEs) are well documented, there is still limited research on their accumulation at trace concentrations in small mammals inhabiting agricultural ecosystems. This study provides the first comprehensive assessment of PHE accumulation in fossorial water voles (Arvicola scherman) from two low-input apple orchards (Nava and Oles) located in Asturias, northwestern Spain, demonstrating its value as a potential bioindicator of trace element inputs. We quantified the concentrations of three toxic metals (Pb, Cd, and Hg) and selenium (Se), an element with concentration-dependent toxicity, in kidney, liver, and muscle tissues. We also determined inter-population differences and associations with body condition. Overall, element concentrations generally reflected the natural content of the local soils, except for Cd in the kidney, which exceeded soil levels, highlighting its strong affinity for this organ. Significant differences in Pb, Cd, and Se accumulation were found among tissues, with the kidney showing the highest levels, underscoring the importance of organ-specific monitoring. The observed positive correlations between body condition and Se and Cd in kidney tissue, and Cd in liver tissue, particularly in the Nava population, suggest that individual health status modulates exposure and accumulation dynamics. Higher PHE burdens were found in Oles specimens, pointing to a potential threshold effect where higher contamination may begin to impair physiological condition. In contrast, Hg showed a negative relationship with body condition, suggesting possible adverse effects even in these low-input systems. These findings highlight the importance of carefully interpreting physiological biomarkers within an ecological context and demonstrate the potential for trace elements to propagate through the food web, with possible cascading effects on predator health and key ecosystem services, such as natural pest control. Future research should extend to more contaminated sites and adopt an integrative framework combining biomonitoring, dietary ecology, and stress physiology to better assess the ecological risks posed by trace elements in agroecosystems.